Remote‐sensing magnetospheric dynamics with riometers: Observation and theory

Liu, W. W.; Liang, J.; Spanswick, E.; Donovan, E.

doi:10.1029/2006ja012115

Cited by 10 publications

(33 citation statements)

References 48 publications

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“… Baker et al [1981] found that riometer absorption can be used as an excellent proxy of substorm high‐energy injection at geosynchronous orbit. A series of recent works have further established the viability of using ground‐based riometer arrays to monitor electron injection [ Spanswick et al , 2005, 2007; Liu et al , 2007]. In particular, Liu et al [2007] (hereinafter referred to as LW07) developed a model of electron injection that predicts the riometer response to magnetospheric dipolarization.…”

Section: Introductionmentioning

confidence: 99%

“…A series of recent works have further established the viability of using ground‐based riometer arrays to monitor electron injection [ Spanswick et al , 2005, 2007; Liu et al , 2007]. In particular, Liu et al [2007] (hereinafter referred to as LW07) developed a model of electron injection that predicts the riometer response to magnetospheric dipolarization. These authors demonstrated that strong electron precipitation is expected to be a by‐product of substorm dipolarization and further investigated in detail how the riometer signal changes during the substorm EP and how the signal intensification is controlled by the magnitude of pitch angle diffusion coefficient.…”

Section: Introductionmentioning

confidence: 99%

“…These authors demonstrated that strong electron precipitation is expected to be a by‐product of substorm dipolarization and further investigated in detail how the riometer signal changes during the substorm EP and how the signal intensification is controlled by the magnitude of pitch angle diffusion coefficient. LW07 is based on a version of the Fokker‐Planck equation wherein the convective transport terms are associated with adiabatic changes imposed on the distribution of riometer electrons by magnetic field dipolarization. The effect of the finite azimuthal extent of the substorm dipolarization region and the eastward curvature/gradient drift of energetic electrons was not included in the model.…”

Section: Introductionmentioning

confidence: 99%

“…The effect of the finite azimuthal extent of the substorm dipolarization region and the eastward curvature/gradient drift of energetic electrons was not included in the model. In other words, LW07 is appropriate for injection events near the center of the dipolarization region, where a quasi‐1‐D approximation is reasonable. The assumption, however, deteriorates progressively as one moves closer to the duskward edge of the substorm current wedge (SCW), where an imbalance (to be discussed later in this paper) associated with adiabatic drift of riometer electrons becomes important.…”

Section: Introductionmentioning

confidence: 99%

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Azimuthal structures of substorm electron injection and their signatures in riometer observations

et al. 2007

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[1] We propose a theoretical model to investigate the effects of the curvature/gradient (c/g) drift and the finite azimuthal extent of the dipolarization region on the electron injection process associated with the substorm dipolarization. We study the azimuthal structure of high-energy (>30 keV) electron precipitation flux and compare the result with riometer observations. We are able to reproduce three basic archetypes of riometer responses to substorms, namely, the spike, dispersionless injection, and dispersed injection events catalogued in previous observations. The electron injection near the duskward edge of the dipolarization region is most subject to azimuthal c/g drift loss, appearing in riometer observations as the ''spike'' feature. The ''dispersionless injection'' response is seen inside the dipolarization region but some distance away from its western border: or, alternatively, when the substorm has a rapid westward expansion, so that the gain and loss of electrons from the duskside and dawnside of a dipolarizing flux tube roughly balance. The ''dispersed injection'' feature is seen east of the dipolarization region. Our theory successfully explains the statistical differences in terms of magnetic local time location and peak intensity between spikes and injection events. Through the substorm event on 23 May 1998 we demonstrate that our theoretical predictions of riometer responses are very consistent with the observations. We highlight the potential of riometers in resolving the azimuthal extent and evolution of the dipolarization region, which provides a new ground-based technique of remote sensing the substorm process.

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Section: Introductionmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

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Azimuthal structures of substorm electron injection and their signatures in riometer observations

et al. 2007

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“…For a number of events, they found that a sharp rise in plasma sheet electron flux for energies >30 keV (dispersionless injection) was often accompanied (under certain conditions) by a sharp rise in riometer absorption due to sudden enhancement of ionization in the lower ionosphere. If multiple riometers pick up this ionospheric signature of high energy particle precipitation, then tracking the movement of these signatures can give insight into the spatial and temporal evolution of the substorm injection region [Berkey et al, 1974;Liang et al, 2007;Liu et al, 2007;Spanswick et al, 2009]. In this study, we extend this ground-based method of identifying substorm precipitation signatures to GPS TEC, assuming that enhanced electron density due to high-energy particle precipitation will produce detectable TEC enhancements.…”

Section: Introductionmentioning

confidence: 99%

GPS TEC technique for observation of the evolution of substorm particle precipitation

et al. 2011

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[1] One of the signatures of magnetospheric substorms is the precipitation of high energy particles into the high latitude ionosphere. In this paper, we introduce a new method of tracking substorm particle precipitation using GPS Total Electron Content (TEC) and provide some preliminary observations of precipitation signatures from application of this method. Using TEC measurements from several GPS receivers, we examined particle precipitation signatures associated with two separate substorm events (4 October 2008 and 29 October 2008) and monitored the expansion of the high energy precipitation regions with a higher temporal and spatial resolution than previously available. For each event we have observed TEC signatures associated with substorm particle precipitation along 20 to 25 separate GPS raypaths from up to 7 GPS receivers located in the Canadian Arctic. This is in addition to particle injection signatures found in CLUSTER satellite data and precipitation signatures in ground based riometer data. Signature timing on different raypaths from different stations indicates a mainly northward (tailward) expansion of the precipitation (injection) region with a smaller westward (azimuthal) component for the events studied. By applying a triangulation method, we also calculated propagation velocity of the precipitation boundary in regions covered by our GPS receivers. For each substorm, expansion velocity ranged from 0.3-2 km/s northward and 0-1 km/s westward, and tended to decrease in magnitude at higher latitudes.

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Energetic electron bursts in the plasma sheet and their relation with BBFs

et al. 2014

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We studied energetic electron bursts (EEBs) (40-250 keV) in the plasma sheet (PS) and their relation to bursty bulk flows (BBFs) using the data recorded by Cluster from 2001 to 2009. The EEBs in the PS can be classified into four types. Three types of EEBs are dispersionless, including EEBs accompanied with BBFs (V > 250 km/s) but without dipolarization front (DF); EEBs accompanied with both dipolarization front (DF) and BBF; and EEBs accompanied with DF and fast flow with V < 250 km/s. One type of EEB, i.e., EEBs not accompanied with BBFs and DFs, is dispersed. The energetic electrons (40-130 keV) can be easily transported earthward by BBFs due to the strong dawn-dusk electric field embedded in BBFs. The DFs in BBFs can produce energetic electrons (40 to 250 keV). For the EEBs with DF and BBFs, the superposed epoch analyses show that the increase of energetic electron flux has two phases: gradual increase phase before DF and rapid increase phase concurrent with DF. In the PS around x = À18 R E , 60%-70% of EEBs are accompanied with BBFs, indicating that although hitherto there have been various acceleration mechanisms of energetic electrons, most of the energetic electrons in the PS are related with magnetic reconnection, and they are produced either directly by magnetic reconnection or indirectly by the DFs within BBFs. In the BBF's braking region of À12 R E < x < À10 R E , 20% of EEBs are accompanied with BBFs. The corresponding ratio between EEBs and BBFs shows a dawn-dusk asymmetry.

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Remote‐sensing magnetospheric dynamics with riometers: Observation and theory

Cited by 10 publications

References 48 publications

Azimuthal structures of substorm electron injection and their signatures in riometer observations

Azimuthal structures of substorm electron injection and their signatures in riometer observations

GPS TEC technique for observation of the evolution of substorm particle precipitation

Energetic electron bursts in the plasma sheet and their relation with BBFs

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